Changes in fatty acid composition of human brain myelin lipids during maturation

Abstract— The variation with age of the fatty acid composition of the major lipids in human brain myelin was compared with that of cerebral white matter from the same region. The myelin was isolated from the semiovale centre of the cerebrum of 27 subjects neonatal to old aged. The phospholipid, cholesterol and galactolipid concentrations were determined in all the samples, as were the proportions of the major phospholipid classes. The proportions of cholesterol and especially of the galactolipids increased in myelin during the first 6 months, and in cerebral white matter up to 2 years. During this period the individual phospholipids also varied substantially. Serine phosphoglycerides and especially sphingomyelins increased, and choline phosphoglycerides decreased. The fatty acid patterns of ethanolamine phosphoglycerides (EPG) and sphingomyelins underwent the largest changes. The proportions of saturated fatty acids in EPG diminished rapidly, and there was an increase of monoenoic acids. Fatty acids of the linoleic acid series showed a peak between 4 and 12 months, after which time their proportion slowly diminished to old age. The major fatty acid of this series was docosatetraenoic acid, 22:4 (n-6), which constituted more than 25% of total fatty acids at the maximum level. The fatty acid changes were larger in cerebral white matter, but from 2 years of age the EPG fatty acid pattern in myelin was similar to that in white matter. The fatty acid changes in serine and choline phosphoglycerides of myelin with maturation were much less striking than in EPG but of a similar type. In myelin sphingomyelin the proportion of saturated long-chain fatty acids, C₁₆-C₂₂, diminished, while that of monoenoic acids increased and continued to do so up to old age. From 2 years of age the fatty acid patterns in myelin and cerebral white matter were quite similar. Also the fatty acid patterns of cerebrosides and sulphatides in cerebral white matter and myelin were the same except for the first 2 months of life. The same fatty acid changes occurred in cerebrosides and sulphatides as in the sphingomyelins, i.e. increased proportions of unsaturated (monoenoic) acids. The proportions of 24:1 and 24h:1 and of the odd-numbered fatty acids 25:1 and 23h:1 continued to increase to old age. The variations of the individual lipid fatty acid patterns were small except in the youngest age classes, in which the variations were presumably ascribable to the difficulty in determining the gestational age.     

CHANGES IN LIPID CONCENTRATIONS AND FATTY ACID COMPOSITIONS IN RAT CEREBRUM DURING MATURATION

Abstract— Rat cerebrum was analysed at 20 different ages from birth to 45 days of age, for its concentration of protein, cholesterol, cerebrosides, phospholipids and gangliosides, and for the concentration of fatty acids of the linoleic and linolenic acid series. The fatty acid patterns of choline phosphoglycerides and ethanolamine phosphoglycerides were determined at the same ages. Phases of rapid accretion were found for protein, phospholipids, gangliosides and cholesterol. The accretion of the fatty acids of the linoleic acid series ceased at 20 days of age, while that of the fatty acids of the linolenic acid series continued. The fatty acid composition of the phosphoglycerides changed during the maturation of rat cerebrum and these changes consisted of chain elongation, increased unsaturation and variation in the pattern of the polyenoic acids. These changes varied irregularly with age and each developmental stage had characteristic fatty acid patterns of choline and ethanolamine phosphoglycerides.     

Concentration and fatty acid composition of cholesteryl esters of normal human brain

Abstract— —Cholesteryl esters were isolated from the cerebral cortex and white matter of human brains at different ages, and their concentration and composition determined. The esters were separated from other lipids by chromatography on silicic acid and finally purified by TLC. The fatty acids were converted to the methyl esters by alkaline trans-methylation and analysed by GLC. A TLC method was elaborated for quantitative determination of small amounts of cholesteryl esters in the presence of free cholesterol. The concentration of cholesteryl esters was only 0·1–0·2 per cent of the total cholesterol content of cerebral tissue in older children and adults. During early myelination the concentration was many times greater, especially in the white matter but it never exceeded 2 per cent of the total cholesterol in any subject. The major fatty acids of human brain cholesteryl esters were oleic, palmitic, palmitoleic and arachidonic acid. After completion of myelination, arachidonic acid constituted the major fatty acid. There were fairly small differences in the fatty acid pattern of the cholesteryl esters between grey and white matter, but the concentration of polyunsaturated fatty acids was larger in the grey matter. Cholesteryl esters appear to play an important role in the metabolism of the phosphoglyceride fatty acids in cerebral tissue.     

Large Alterations in Ganglioside and Neutral Glycosphingolipid Patterns in Brains from Cases with Infantile Neuronal Ceroid Lipofuscinosis/Polyunsaturated Fatty Acid Lipidosis

Lipid composition was studied on cerebral tissue from nine children who had died of a progressive encephalopathy called the infantile form of neuronal ceroid lipofuscinosis (INCL) or polyunsaturated fatty acid lipidosis (PFAL). In the terminal stage of the disease, the concentrations of all lipid classes were found to be significantly reduced in the cerebral and cerebellar cortex and white matter. The concentration of gangliosides of the cerebral cortex was 15% and that of cerebrosides (galactosylceramide) in white matter 0.2-5% of the normal values for the children's ages. The reduction of gangliosides mainly affected those of the gangliotetraose series, particularly GD1a. The fatty acids of the linolenic acid series were strongly reduced in ethanolamine and serine phosphoglycerides. A very large increase up to 100-fold of oligoglycosphingolipids of the globo series and two fucose-containing lipids of the neolacto series was found in the forebrain of the three advanced cases examined. The brain tissue also contained very high concentrations of mono-, di-, and trisialogangliosides of the lacto and neolacto series, gangliosides with type 1 chain dominating. The structures of the gangliosides were tentatively identified by gas chromatography-mass spectrometry and monoclonal antibodies with carefully determined epitope specificity. The gangliosides and neutral glycosphingolipids had very similar fatty acid composition, consisting of about 40% stearic acid and 40% C24-acids.     

Dietary effects on brain fatty acid composition: the reversibility of n-3 fatty acid deficiency and turnover of docosahexaenoic acid in the brain, erythrocytes, and plasma of rhesus monkeys

Rhesus monkeys given pre- and postnatal diets deficient in n-3 essential fatty acids develop low levels of docosahexaenoic acid (22:6 n-3, DHA) in the cerebral cortex and retina and impaired visual function. This highly polyunsaturated fatty acid is an important component of retinal photoreceptors and brain synaptic membranes. To study the turnover of polyunsaturated fatty acids in the brain and the reversibility of n-3 fatty acid deficiency, we fed five deficient juvenile rhesus monkeys a fish oil diet rich in DHA and other n-3 fatty acids for up to 129 weeks. The results of serial biopsy samples of the cerebral cortex indicated that the changes of brain fatty acid composition began as early as 1 week after fish oil feeding and stabilized at 12 weeks. The DHA content of the phosphatidylethanolamine of the frontal cortex increased progressively from 3.9 +/- 1.2 to 28.4 +/- 1.7 percent of total fatty acids. The n-6 fatty acid, 22:5, abnormally high in the cerebral cortex of n-3 deficient monkeys, decreased reciprocally from 16.2 +/- 3.1 to 1.6 +/- 0.4%. The half-life (t 1/2) of DHA in brain phosphatidylethanolamine was estimated to be 21 days. The fatty acids of other phospholipids in the brain (phosphatidylcholine, -serine, and -inositol) showed similar changes. The DHA content of plasma and erythrocyte phospholipids also increased greatly, with estimated half-lives of 29 and 21 days, respectively. We conclude that monkey cerebral cortex with an abnormal fatty acid composition produced by dietary n-3 fatty acid deficiency has a remarkable capacity to change its fatty acid content after dietary fish oil, both to increase 22:6 n-3 and to decrease 22:5 n-6 fatty acids. The biochemical evidence of n-3 fatty acid deficiency was completely corrected. These data imply a greater lability of the fatty acids of the phospholipids of the cerebral cortex than has been hitherto appreciated.     

THE DISTRIBUTION OF LIPIDS IN THE HUMAN NERVOUS SYSTEM-V. GANGLIOSIDES AND ALLIED NEUTRAL GLYCOLIPIDS OF INFANT BRAIN

—Gangliosides and allied neutral glycosylceramides were isolated from human infant (2-24 months of age) cerebral cortex and white matter. The individual glycolipids were separated quantitatively by a combination of column and thin-layer chromatographic methods on silica gel, DEAE-cellulose and Sephadex G-25. In cerebral cortex G_D1a and G_M1 were the major fractions and constituted more than 70 per cent of the total gangliosides. The concentrations of neutral glycolipids, except for galactosylceramides, were very low: lactosylceramide and glucosylceramide comprised 30 and 5 nmol/g wet weight, respectively. In white matter their concentrations were 10 times higher. The ganglioside concentration was only 50 per cent of that in cerebral cortex: the difference was accounted for mainly by the much lower content of the major di- and trisialogangliosides. Stearic acid was the predominant fatty acid of all brain gangliosides. G_M3, and G_D3 had a considerable content of the very long-chain fatty acids, C₂₂-C₂₄, particularly in the white matter. Glucosylceramide and lactosylceramide had almost identical fatty acid patterns between each other in cerebral cortex and white matter. In the cerebral cortex stearic acid and in the white matter the very long-chain acids predominated. d20:1 Sphingosine comprised more than 20 per cent of total sphingosine in all the gangliosides of the G_l- and G₂-series. G_M3, and G_D3 like lactosylceramide contained significantly less of d20:1 sphingosine. The findings suggest the existence of separate compartments for the biosynthesis of the gangliosides. Glucosylceramides and lactosylceramides of white matter have the same ceramide composition as the galactosylceramides with normal fatty acids and are thus unlikely to be intermediates in the metabolism of the major brain gangliosides which have a completely different fatty acid composition.     

Changes in the fatty acid profiles of red blood cell membrane phospholipids in human neonates during the first month of life

We have studied the changes in the fatty acid profiles of red blood cell membrane phospholipids in 47 infants who were exclusively fed human milk from birth to 1 month of life. Twenty blood samples were obtained from cord, 15 at 7 days and 12 at 30 days after birth. Membrane phospholipids were obtained from erythrocyte ghosts by thin-layer chromatography and fatty acid composition was determined by gas liquid chromatography. Phosphatidylcholine showed the most important changes during early life; stearic, w6 eicosatrienoic and arachidonic acids decreased whereas oleic and linoleic acids increased. In phosphatidylethanolamine, palmitic and stearic acid declined and oleic, linoleic and docosahexenoic acids increased with advancing age. Small changes were noted for individual fatty acids in phosphatidylserine. In sphingomyelin stearic acid increased from birth to 1 month and linoleic, arachidonic and nervonic acids decreased. Total polyunsaturated fatty acids of the w6 series greater than 18 carbon atoms increased with advancing age in phosphatidylethanolamine and decreased in choline and serine phosphoglycerides and in sphingomyelin. Long chain fatty acids derived from linoleic acid decreased in phosphatidylcholine but increased in ethanolamine and serine phosphoglycerides. The different behavior in the changes observed in fatty acid patterns for each erythrocyte membrane phospholipid may be a consequence of its different location in the cell membrane bilayer and specific exchange with plasma lipid fractions.     

Altered Composition of Cerebral Microvessel Membrane Phosphoglycerides from Senescent Mouse

Abstract— Phosphoglyceride and fatty acid composition was determined in the cellular membranes of isolated cerebral microvessels and brain parenchymal cells (neurons and glia) taken from 10-, 20-, and 27–30-month-old C57BL6/NNIA mice. Lipids were extracted from each fraction and the fatty acid profiles of ethanolamine, cho-line, serine, and inositol phosphoglycerides analyzed by gas chromatography. The results suggest that membrane phosphoglycerides from cerebral microvessels are significantly more affected by the aging process than are those of the brain parenchyma. Relative percentage for fatty acids in cerebral microvessels indicate an overall decline in membrane unsaturation with a concomitant elevation in the level of saturation. The decline in unsaturation is reflected primarily in the loss of precursor fatty acids for arachidonic (18:2n-6 and 20:3n-6) and docosahexaenoic (20:5n-3 and 22:5n-3) acids. Levels of arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acids in each phos-phoglyceride remained unchanged with age; however, mol% for ethanolamine plasmalogen, a major source of these fatty acids, was significantly reduced in 27–30-month-old mice. Conversely, mol% for choline phospho-glyceride increased with age. The age-related changes in fatty acid profile for microvessel membrane phosphoglycerides are reflected by increased saturation/unsaturation ratios and decreased unsaturation indices. These parameters were not affected by aging in parenchymal membranes.     

Fatty acid composition of cholesterol esters in brains of patients with Schilder's disease, G M1 -gangliosidosis and Tay-Sachs disease, and its possible relationship to the -position fatty acids of lecithin

Abstract— Cholesterol esters were isolated from cerebral cortex and white matter of patients with Schilder's disease, G_M1-gangliosidosis and Tay-Sachs disease, and the fatty acid composition was determined by gas-liquid chromatography. The fatty acid composition was similar among the three pathological conditions, but it was entirely different from that reported for cholesterol esters of normal brain. Lecithin and ethanolamine phospholipids were isolated from the same brain specimens, treated with snake venom phospholipase A, and the fatty acids at the a’and β-positions of the glycerol moiety were determined separately. The fatty acid composition of cholesterol esters was similar to that of the β-position fatty acids of lecithin of white matter in all samples, and was quite different from those of the a'-position of lecithin, or of the a’or β-position of ethanolamine phospholipids. The results indicate that the source of fatty acids for cholesterol esterification in nonspecific sudanophilic demyelination is different from that in normal brain, and that the most likely source is the β-linked fatty acids of lecithin. There are two possible enzymic mechanisms; activation of phospholipase A and subsequent esterification of the liberated β-position fatty acids to cholesterol, or direct transacylation by lecithin-cholesterol acyl transferase.     

Positional Distribution of Acyl and Alk-1-enyl Groups in Grey and White Matter Ethanolamine and Choline Phosphoglycerides of a Marsupial, the Koala (Phascolarctos cinereus)

The major phosphoglycerides in grey and white matter from the brain of the koala have been separated and examined. The major polyunsaturated fatty acids present in both the diacyl- and alk-1-enyl acylglycerophosphorylethanolamines from grey matter were 22:6 omega 3, 20:4 omega 6, and 22:4 omega 6. In both grey and white matter, 22:6 omega 3 and 20:4 omega 6 were concentrated in the 2-position of diacylglycerophosphorylethanolamines and 22:4 omega 6 in the 2-position of alk-1-enylacylglycerophosphorylethanolamines; polyunsaturated fatty acid levels were higher in diacylglycerophosphorylethanolamines. Ethanolamine phosphoglyceride fractions from grey matter were enriched in polyunsaturated fatty acids compared with those from white matter. The acyl groups 18:0, 18:1, and 16:0 and their alk-1-enyl analogues were prominent in grey and white matter ethanolamine phosphoglycerides; 18:1 was dominant in white matter alk-1-enylacylglycerophosphorylethanolamines. The plasmalogen composition of ethanolamine phosphoglycerides was 55% in grey matter and 76% in white matter. Choline phosphoglycerides contained negligible plasmalogen and low polyunsaturated fatty acid levels. Diacylglycerophosphorylcholine was characterized by high levels of 16:0 and 18:1. Similar acyl group distributions were estimated in the 1-position in both grey and white matter, 16:0 being present at greater than 50%. The presence of the molecular species 18:0/22:6 omega 3 was indicated in grey matter diacylglycerophosphorylethanolamine, 18:1/18:1 in white matter alk-1-enylcylglycerophosphorylethanolamine, and 16:0/18:1 in white matter diacylglycerophosphorylcholine.     

Specific phospholipid fatty acid composition of brain regions in mice. Effects of n-3 polyunsaturated fatty acid deficiency and phospholipid supplementation

This study examined the effects of dietary alpha-linolenic acid deficiency followed or not by supplementation with phospholipids rich in n;-3 polyunsaturated fatty acid (PUFA) on the fatty acid composition of total phospholipids in 11 brain regions. Three weeks before mating, mice were fed a semisynthetic diet containing both linoleic and alpha-linolenic acid or deficient in alpha-linolenic acid. Pups were fed the same diet as their dams. At the age of 7 weeks, a part of the deficient group were supplemented with n;-3 polyunsaturated fatty acids (PUFA) from either egg yolk or pig brain phospholipids for 2 months. Saturated and monounsaturated fatty acid levels varied among brain regions and were not significantly affected by the diet. In control mice, the level of 22:6 n-3 was significantly higher in the frontal cortex compared to all regions. alpha-Linolenic acid deficiency decreased the level of 22:6 n-3 and was compensated by an increase in 22:5 n-6 in all regions. However, the brain regions were affected differently. After the pituitary gland, the frontal cortex, and the striatum were the most markedly affected with 40% reduction of 22:6 n-3. Supplementation with egg yolk or cerebral phospholipids in deficient mice restored a normal fatty acid composition in brain regions except for the frontal cortex. There was a regional distribution of the fatty acids in the brain and the impact of deficiency in alpha-linolenic acid was region-specific. Dietary egg yolk or cerebral phospholipids are an effective source of n-3 PUFA for the recovery of altered fatty acid composition induced by a diet deficient in n-3 PUFA.     

THE EFFECT OF DIFFERENT DIETARY LEVELS OF ESSENTIAL FATTY ACIDS ON LIPIDS OF RAT CEREBRUM DURING MATURATION1

Abstract— Three dietary levels of essential fatty acids, 30, 0-75 and 007 calorie-%, with a linoleic: linolenic acid ratio of 4:1, were fed to rats for two generations. In the third generation the weight of the cerebrum and the concentration of its lipids and the fatty acid composition of phosphoglycerides were determined from term to 120 days of age. The cerebral weights and the concentrations of phospholipids, cholesterol and cerebrosides differed only slightly between the three dietary groups. The accretion of fatty acids of the linoleic acid series was independent of the dietary essential fatty acid level while the accretion of fatty acids of the linolenic acid series was markedly reduced in the groups with low essential fatty acid supply. The sum of the total polyunsaturated fatty acids in ethanolamine phosphoglycerides differed only slightly between the groups. The proportion of the major polyunsaturated fatty acid of the linoleic acid series was equal between the groups while that of 22:6 (n-3) was much lower in the groups fed 007 calorie % essential fatty acids. In these latter groups the relative concentrations of 22:5 (n-6), 20:3 (n-9) and 22:3 (n-9) were increased. The differences in the fatty acid composition were dependent on the age of the rats. They were largest in newborn rats and diminished with age after weaning.     

Effect of temperature acclimatization on the fatty acid composition of goldfish intestinal lipids

1. The fatty acid composition of whole goldfish, whole-intestinal mucosa, intestinal mucosal membranes and individual phospholipids extracted from mucosal membranes were measured, fish adapted to different temperatures being used. 2. Alterations of the adaptation temperature did not noticeably affect the fatty acid composition of the whole-fish lipids, but there were marked changes in the fatty acids of lipids extracted from homogenates of goldfish intestinal mucosa. These changes were more pronounced in a membrane fraction prepared from these homogenates. Raising the adaptation temperature by 20 degrees C halved the percentage of C(20:1), C(20:4) and C(22:6) fatty acids and nearly doubled the percentage of C(18:0) and C(20:3) fatty acids recovered. 3. Choline phosphoglycerides constituted about one-half and ethanolamine phosphoglycerides about one-quarter of the total membrane phospholipids. 4. The fatty acids of choline and ethanolamine phosphoglycerides were more susceptible to temperature-dependent changes than were the phosphoglycerides of inositol or serine. 5. The increase in C(18:0) fatty acid that occurred in membranes of warm-adapted fish was greatest for ethanolamine phosphoglycerides, but increases also occurred in other phospholipid fractions and in membrane neutral lipids.     

Phospholipid supplementation reverses behavioral and biochemical alterations induced by n-3 polyunsaturated fatty acid deficiency in mice

This study investigated the effects of a diet deficient in alpha-linolenic acid followed or not by supplementation with phospholipids rich in n-3 polyunsaturated fatty acids (PUFA) on behavior and phospholipid fatty acid composition in selected brain regions. Three weeks before mating, two groups of mice were fed a semisynthetic diet containing both linoleic and alpha-linolenic acid or a diet deficient in alpha-linolenic acid. Pups were fed the same diet as their dams. At the age of 7 weeks, a part of the deficient group was supplemented with n-3 PUFA from either egg yolk or pig brain phospholipids for 2 months. In the open field, rearing activity was significantly reduced in the deficient group. In the elevated plus maze (anxiety protocol), the time spent on open arms was significantly smaller in deficient mice than in controls. Using the learning protocol with the same task, the alpha-linolenic acid deficiency induced a learning deficit. Rearing activity and learning deficits were completely restored by supplementation with egg yolk or cerebral phospholipids, though the level of anxiety remained significantly higher than that of controls. There were no differences among the 4 diet groups for either the Morris water maze or passive avoidance. In control mice, the level of 22:6 n-3 was significantly higher in the frontal cortex compared to all other regions analysed. The frontal cortex and the striatum were the most markedly affected by the deficiency. Supplementation with phospholipids restored normal fatty acid composition in brain regions except for frontal cortex. Egg yolk or cerebral phospholipids are an effective source of n-3 PUFA for reversing behavioral changes and altered fatty acid composition induced by a diet deficient in n-3 PUFA.     

DEVELOPMENTAL PROFILES OF GANGLIOSIDES IN HUMAN AND RAT BRAIN

Abstract— The developmental profiles of individual gangliosides of human brain were compared with those of rat brain. Interest was focused mainly on the pre- and early postnatal development. Human frontal lobe cortex covering the period from 10 foetal weeks to adult age and the cerebrum of rat from birth to 21 days were analysed. Lipid-NANA and lipid-P were followed; in the rat, also protein and brain weight. A limited number of samples of human cerebral white matter and cerebellar cortex were also studied. The following major results were obtained:

• 1 The ganglioside concentration increased approximately three-fold within a short period: in rat cerebrum, from birth to the 17th day; in human cerebral cortex, from the 15th foetal week to the age of about 6 months. The largest increase in the rat brain occurred by the 11th to the 13th day; in human brain by term. The relative increase of gangliosides during this period was more rapid than that of phospholipids.
• 2 A hitherto unknown distinct early period of ganglioside and phospholipid formation in rat occurred by the second to fourth day.
• 3 The changes in brain ganglioside pattern, characteristic of the developmental stages of the rat, were found to be equally pronounced in the human brain.
• 4 Regional developmental differences in the ganglioside pattern were demonstrated in human brain. A characteristic white matter pattern, rich in monosialogangliosides, had developed by the age of 1 year. The increase in ganglioside concentration and the formation of the definitive ganglioside pattern of cerebellar cortex occurred later than in cerebral cortex. This cerebellar pattern was characterized by a very large trisialoganglioside fraction.
• 5 The two periods of rapid ganglioside metabolism in rat brain preceded the two periods of rapid protein biosynthesis.

     

LIPID COMPOSITION IN GRAY AND WHITE MATTER OF THE BRAIN IN MENKES' DISEASE

Abstract— Lipid composition has been determined in brain frontal lobe gray and white matter from a 5-month-old patient who died from Menkes' disease, and from a normal control patient of the same age.
Total cholesterol and the amount of cholesterol esters were significantly increased in the case of Menkes' disease, whereas the values for free cholesterol were nearly unchanged.
In white matter a decrease in total galactolipids was observed in the pathological brain.
The values for total phospholipids were unchanged for the tissues, but the ratio between phosphatidylcholines and phosphatidylethanolamines (including ethanolamineplasmalogens) in white matter from the patient seemed increased. The fatty acid pattern of phosphatidylethanolamines (including ethanolamineplasmalogens), phosphatidylcholines and sphingomyelin were similar to those of the normal control. Phosphatidylethanolamines from pathological tissues contained 25–30 per cent polyunsaturated fatty acids with four, five or six double bonds.     

Lipid metabolism in brain tissue explants

Abstract— Tissue explants from frontal lobes of rat brain were used for the study of cerebral fatty acid metabolism. After tissues had been maintained in serum-supplemented medium, a lipid-free medium was substituted and metabolic studies were carried out. Under these conditions explants continued to take up lipid precursors for at least 48 h, as judged by incorporation of dl -[2-¹⁴C]mevalonic acid into cellular lipids. [l-¹⁴C]Stearic acid and [l-¹⁴C]palmitic acid were bound to cells as the free fatty acids, or incorporated into neutral lipids (particularly triglycerides), glycolipids and phospholipids. In the galactolipid fraction, cerebrosides were the principal radioactive lipids. Choline phosphoglycerides, ethanolamine phosphoglycerides, inositol phosphoglycerides and serine phosphoglycerides were the principal radioactive phospholipids. Fatty acids were incorporated into cellular lipids either unchanged or after desaturation, chain elongation, or both. Maximum incorporation of stearate occurred in tissues derived from 3-day-old animals. With increasing age the uptake of fatty acid dropped sharply. When the labelling of lipids as a function of time was followed in 3-day-old animals, triglycerides and choline phosphoglycerides were the first fractions to take up labelled stearate. Labelling of cerebrosides occurred slowly, only becoming evident after 24 h. These studies exemplify the usefulness of tissue explants for prolonged metabolic studies in normal and pathological specimens of brain.     

THE FATTY ACID COMPOSITION OF PHOSPHOLIPIDS AND GLYCOLIPIDS IN JIMPY MOUSE BRAIN

Abstract— Phospholipids and sphingolipids from brains of normal and Jimpy mice were isolated in a pure form by thin-layer chromatographic procedures. The fatty acid composition of the major phospholipids, i.e. ethanolamine glycerophospholipids, serine glycerophospholipids, choline glycerophospholipids and inositol glycerophospholipids, as well as sphingomyelin, cerebrosides and sulphatides was determined by gas-liquid chromatography. A specific fatty acid pattern for each of the four glycerophospholipids was found. The fatty acid composition of inositol glycerophospholipid, which has not previously been studied in mouse brain, was characterized by a high concentration of arachidonic acid. After 16 days of age, fatty acid analysis showed definite differences between the phospholipids from normal and mutant brains. A small increase of polyunsaturated fatty acids in glycerophospholipids of ethanolamine, serine and choline from the Jimpy central nervous system was found, which has been explained by the myelin deficiency. Sphingomyelin, cerebrosides and sulphatide analyses showed a wide distribution of saturated and mono-unsaturated fatty acids in both normal and mutant mice. A reduction in the amount of long-chain fatty acids was demonstrated in mutant brain sphingolipids; in sulphatides and cerebrosides, the amount of non-hydroxy fatty acids was reduced to a greater extent than in sphingomyelin. The distribution of fatty acids in sphingolipids from the myelin and microsomal fractions was also investigated in both types of mice. Cerebrosides were characterized by a high content of long-chain fatty acids in myelin as well as in microsomes. Sulphatides and sphingomyelin, on the other hand, showed a higher content of medium-chain fatty acids in microsomes than in myelin. In the mutant brain, the amount of long-chain fatty acids was reduced in both subcellular fractions. The deviation from normal in the pattern of fatty acid distribution in Jimpy brain is discussed in relation to the current concepts of glycolipid biosynthesis.     

Phospholipids and acyl groups in subcellular fractions from human cerebral cortex

Subcellular fractionation of human brain cortex obtained at autopsy yielded microsomal and synaptosome-rich fractions from the gray matter and microsomal and purified myelin fractions from the white matter. The phospholipids of myelin were high in plasmalogens, and the molar ratio of alkenyl acyl sn-glycero-3-phosphorylethanolamine to diacyl sn-glycero-3-phosphorylethanolamine was 4. The acyl groups of the myelin phosphoglycerides were enriched in monoenes (mainly 18:1 and 20:1) and a tetraene, 22:4(n - 6). The phospholipids in the synaptosome-rich fraction were high in diacyl sn-glycero-3-phosphorylcholine, and the molar ratio of the alkenyl acyl sn-glycero-3-phosphorylethanolamine to diacyl sn-glycero-3-phosphorylethanolamine was 0.88. The acyl groups of synaptosomal ethanolamine phosphoglycerides were rich in 22:6(n - 3) but contained a very low amount of 20:1. The lipid composition of microsomes from the gray matter was different from that of microsomes from the white matter but was nearly identical with that of the synaptosome-rich fraction. Except for a slightly lower proportion of alkenyl acyl sn-glycero-3-phosphorylethanolamine and sphingomyelin, the lipid composition of microsomes from the white matter was also similar to that of the myelin. There were also species-related differences between the brain lipid composition of human and subhuman primates and that of the rodents. Furthermore, the brain lipid composition in normal human subjects is rather constant and does not seem to be affected much by individual variations.     

Brain Cortical Fatty Acids and Phospholipids During and Following Complete and Severe Incomplete Ischemia

Abstract: To explore the possibility that peroxtdative degradation of brain tissue lipid constituents is an important mechanism of irreversible ischemic damage, we measured cortical fatty acids and phospholipids during reversible brain ischemia in the rat. Neither complete nor severe incomplete ischemia (5 and 30 min) caused any measurable breakdown of total or individual fatty acids or phospholipids. Except for a small (and reversible) decrease of inositol plus serine phosphoglycerides in the early postischemic period following 30 min of incomplete ischemia, there were no significant losses of fatty acids or phospholipids during recirculation. Since peroxidation, induced in brain cortical tissue in vitro , characteristically involves degradation of polyenoic fatty acids (arachidonic and docosahexaenoic acids) and of ethanolamine phosphoglycerides, the present in vivo results fail to support the hypothesis that peroxidation of membrane lipids is of primary importance for ischemic brain cell damage. Both complete and severe incomplete ischemia caused a similar increase in the tissue content of free fatty acids (FFA). Thus the FFA pool increased by about 10 times during a 30-min ischemic period, to constitute 1 - 2% of the total fatty acid pool. Since there was a relatively larger increase in polyenoic FFA (especially in arachidonic acid) than in saturated FFA, the release of FFA may be the result of activation of a phospholipase A₂ unbalanced by reesterification. Increased levels of FFA persisted during the initial recirculation period, but a gradual normalization occurred and the ischemic changes were essentially reversed at 30 min after restoration of circulation. The pathophysiological implications of the changes in FFA are discussed with respect to mitochondrial dysfunction, formation of cellular edema and prostaglandin-mediated deterioration of postischemic circulation.